Determination of tin in cast iron and steel



to 12%, desirably 10% antimony,

Patented Sept. 5, 1944 DETERMNATION F 7 AND swan TIN IN CAST IRON Edward T. Saxer, Brecksville, and Robert Minto, Cleveland, Ohio Application September 29', 1941, Serial No. 412,810

' No Drawing.

7 Claims.

of the time required for the determination and the attainment of greater accuracy considering the time required. I I

An important factor in the accomplishment of the foregoing objects is the provision of an im'- proved reagent, for use in the process. Otherv objects will become apparent as the description proceeds.

We are aware that prior to our invention,

chemists have used a number of metals as reducing agents in the determination of tin. In the.

case of aluminum, the action is too, violent and the reduction may go allthe wayto the metal to an extent to give too low values. In the cases of nickel and lead, the action istoo slow. .Ironnails have been used but they are .-'too soluble and too much iron goes intosolutioni Less soluble forms of iron such as electrolytic iron squares are better and have beenused. Powdered antimony has been usedfbut its action is undesir ably slow.

We have now discovered that 'very excellent results can be obtained by a process making use of a granular material composed of iron and I antimony for reducing stannic chloride to stannous chloride.

The process consists essentially in the following steps:

(1) Dissolving the specimen. (2) Precipitating the tin as tin hydroxide.

(3) Redissolving the tin as tin chloride by HCl.

(4) Reducing stannic tin to stannous tin. .(5) Titrating the stannous tin-to determine the amount present.

"In the fourth step, the reagent employed is a granular material consisting of 'iron or steel and antimony, which we call Stanreduce." The Stanreduce should contain substantially no carbon and not less than 3% nor more than 30% antimony, remainder substantially all iron. Inert materials and harmless impurities may be present. Better' results are had between the limits 5% and 15% antimony, and we prefer to use 8% remainder iron or low carbon steel. The iron-antimony reagent marked green coloration of the solution.

reacts with HCl giving off hydrogen which effects I the reduction of stannic chloride and provides a non-oxidizing atmosphere. The percentage of antimony should be such thatthe evolution of hydrogen will be adequate to provide a nonoxidizing atmosphere over the solution during the reduction but high enough in antimony to prevent solution of iron at a rate to cause a The iron-antimony reagent (Stameduce) may be prepared by melting theiron and antimony together, pouring the melt in a thin stream-into water andgranulating the resulting brittle alloy by any suitablecrushing or grinding means.

The folioviingii specific example will serve to illustrate-theinvention. The example takes the -f ormof directions for laboratory procedure, the term Stanreduce meaning therein a 10% antimon'y, v90.7b.,ig3inmaterial.in the form of granules of about 50 ."mes'h. (The granule size is not' critical, however, it may be desirably from about EXAMPLE ms of thesampie into a 300- l. Weigh J 2. add- 50 mm ters r; 1101 (251) and keep at boilingftempratujreruntil the sample is dissolved. The acid residue from a-sulfur determination may be used. Samples of cast iron should m filtered and washed with hot I-ICl solution.

3. Add 100 milliliters of a solution containing 10 grams of NHrCl and 10 milliliters of concentrated NH4OH. If some Fe(0H)a separates, redissolve with a few drops of HCl.

4. Add concentrated NH4OH dropwise until a slight precipitate of Fe(OH) 3 is discernible. This precipitate should be brown and not green.

5. Adda small quantity of paper pulp and replace the flask on the hot plate; bring contents to a boil.

6. Remove flask from hot plate; filter through a ll-centimeter No. l Whatman filter paper, using a filtering flask and gentle suction. Wash flask only sufliciently to remove the paper pulp.

'7. Place the tunnel containing the precipitate ina funnel stand and dissolve the precipitate oil? 1 the paper with repeated washings of hot HCl a boil. Boil gently for 3 minutes. If the tin content is above 0.10 per cent about five minutes may be required to reduce all of the tin.

9. Remove the flask from the hot plate, tighten the stopper, cover the capillary tube with a rubber policeman, and place the flask in a cold water bath until the contents are at room temperature.

10. Add 10 milliliters of starch solution to a clean 300-milliliter Erlenmeyer flask. Decant the c001 solution carefully into this flask, wash the original flask once with water, and add to the titrating flask. Titrate immediately with iodate solution to a permanent blue.

A blank should be run and deducted from this titration.

11. Compute the percentage tin as follows:

Ix S=per cent tin where:

I=Milliliters iodate-blank S=Per cent tin value of 1 milliliter.

SOLUTIONS Standard tin solution Standard potassium iodate solution The same solution as used for sulfur in steel is employed. This is a 0.0156 N iodate solution.

. Grams Kl 2.97 KIOa 0.4955 NaOH .;l;... 0.25

Dissolve ina small amount of water and dilute to 1 liter. The'NaOH must be added to the KI and K103 before adding water for best results.

More KIO: must be used if the salts are old and slightly decomposed.

1 milliliter=.005% S on a 5 gram sample 1 milliliter.=.0185%' Sn on a 5 gram sample 1 milliliter=1000926 gram Sn (theoretical).

Ammonium chloride-Ammonia solution NHiCl grams 100 (NI-IUzSzOa d 0.5 NH4OH "milliliters" 100 Dilute to 1 liter with water.

The ammonium persulphate is added to make certain that a small amount of ferric iron is present to precipitate as Fe(OH)3 in procedure No. 4 of the method of analyses. It is not necessary where samples are dissolved directly in open flasks, but it is necessary when the residue from a sulfur determination is used as a sample.

A Standardizing Weigh 5 grams of Fe (byhydrogen) into a 300- milliliter Erlenmeyer flask. Pipette exactly 5 milliliters of the standard tin solution into this flask 0.005 (titration-blank) X 20 Sn value of 1 milliliter of iodate expressed in per cent when a 5 gram sample is used This has been found to be about 0.021 per cent and not 0.0185 per cent (theoretical).

What we claim is:

1. In a method for determining tin, forming a solution of the tin in HCl and reducing the stannic tin in said solution by introducing thereinto material essentially consisting of iron and antimony in proportion to evolve hydrogen to provide a nonoxidizing atmosphere over the sample while avoiding solution of iron at a rate to produce a marked green color in the solution.

2. In a method for determining tin in a HCl solution containing tin at least partly in the form of stannic chloride, the step of reducing the stannic chloride to stannouschloride by introducing. into the solution a reducing agent essentially consisting of iron and antimony in proportion from 3% to antimony.

3. In a method for determining tin in a HCl solution containing tin at least partly in the form 01 stannic chloride, the step of reducing'the stan nic chloride to stannous chloride by introducing intothe solution a reducing agent essentially consisting of iron and antimony in proportion from 3% to 30% antimony and in a state to present a specific surface equivalent to granular material from 8 mesh to mesh.

4. In a method for determining tin in a HCl solution containing tin at least partly in the form of stannic chloride, the step of reducing the stannic chloride to stannous chloride by introducing into the solution a reducing agent essentially consisting of iron and antimony in proportion from 5% to 15% antimony.

5. In a method for determining tin in a K01 solution containing tin at least partly in the form of stannic chloride, the step of reducing the stannic chloride to stannous chloride by introducing into the solution a reducing agent essentially consisting of iron and antimony in proportion from 5% to 15% antimony and in a state to present a specific surface equivalent 'to granular material from 8 mesh to 100f'inesh.

6. In a method for determining tin in a HCl solution containing tinat least partly in the form of stannic chloride, the step of reducing the stannic chloride to stannous'chloride by introducing into the solution a reducing agent essentially consisting of iron and antimony in proportion from 8% to 12% antimony. v

7. In a method for determining tin in a HCl solution containing tin at least partly in the form of stannic chloride, the step of reducingathe stannic chloride to stannous chloride by introducing into the solution a reducing agent essentially consisting of iron and antimony in proportion from 8% to 12% antimony and in a state to present a, specific surface equivalent to granular material from 8 mesh to 100 mesh.

EDWARD T. SAXER. ROBERT E. MINTO. 

